Create a WebSocket connection between LiveDebugger and debugged browser window

[kraleppa]

We start to have many interactions between LiveDebugger and debugged browser window. We are already sending messages associated with highlighting, but they are handled via standard websocket connection of debugged LiveView process (we just send an event in quite illegal way)

Finding successor and inspecting nodes will require communication in opposite direction (from browser to server) which shouldn't be handled via debugged app websocket connection.

To isolate LiveDebugger communication with the browser and simplify it we have to create a new websocket connection in client.js and create an easy API to send events from the browser to the server and from server to the browser.

The goal here is to:

• create websocket connection in client.js
• create API for it